Process for removing oxygenated contaminates from an ethylene stream

ABSTRACT

The present invention is, in a first embodiment, a process for removing oxygenated contaminants from an ethylene stream comprising: a) providing a dried ethylene stream (A) comprising essentially ethylene, up to 1 w % oxygenates, ethane, CO, CO2, H2, CH4 and C3+ hydrocarbons, b) sending said stream (A) to a stripper (also referred to as a demethanizer) to produce an overhead stream comprising essentially CO, H2 and CH4, a bottom stream comprising essentially ethylene, oxygenates, ethane, CO2 and C3+ hydrocarbons, c) sending said bottom stream of step b) to a deethanizer to produce a bottom stream comprising essentially ethane, oxygenates and C3+ hydrocarbons, an overhead stream consisting essentially of ethylene and CO2, d) sending said overhead of step c) to a fixed bed CO2 adsorption zone to recover an ethylene stream essentially free of CO2. In another embodiment the CO2 adsorption zone can be located at the inlet of the deethanizer. In another embodiment the demethanizer is replaced by two demethanizers. In another embodiment the the deethanizer is replaced by two C2 splitters.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.14/235,251, filed on Apr. 20, 2014, now U.S. Pat. No. 9,701,598, whichclaims the benefit of PCT/EP2012/063754, filed on Jul. 13, 2012, whichclaims priority from EP 11290350.5, filed on Jul. 28, 2011, all of whichare incorporated herein by reference in their entireties for allpurposes.

FIELD OF THE INVENTION

The present invention is a process for removing oxygenated contaminantsfrom an ethylene stream.

Olefins are traditionally produced from petroleum feedstocks bycatalytic or steam cracking processes. These cracking processes,especially steam cracking, produce light olefin(s), such as ethyleneand/or propylene, from a variety of hydrocarbon feedstock. Ethylene andpropylene are important commodity petrochemicals useful in a variety ofprocesses for making plastics and other chemical compounds. The limitedsupply and increasing cost of crude oil has prompted the search foralternative processes for producing hydrocarbon products.

Olefins can be produced by dehydration of the corresponding alcohol.Ethanol can be obtained by fermentation of carbohydrates. Made up oforganic matter from living organisms, biomass is the world's leadingrenewable energy source. The effluent produced by the ethanoldehydration comprises essentially unconverted ethanol, water, ethylene,acetaldehyde. Acetaldehyde may cause problems in ethylene recoveryoperations. It may comprise also very small amounts of ethane, CO, CO2,H2, CH4 and C3+ hydrocarbons. The weight ratio ofethane+CO+CO2+H2+CH4+C3+ hydrocarbons to ethylene is most of time lessthan 20/80.

BACKGROUND OF THE INVENTION

US 20030098281 A1 describes a method of controlling water and/oroxygenate concentrations of an olefin stream. The method includescontacting the olefin stream with a liquid absorbent. The liquidabsorbent is selected from the group consisting of a polyol, amine,amide, nitrile, heterocyclic nitrogen containing compound, and mixturesthereof. A gaseous stream comprising essentially steam, ethylene,propylene and less than 2 w % of oxygenates is condensed in a quenchtower. The overhead of said quench tower is washed with a causticsolution to remove CO2 and then contacted with the liquid absorbent toremove the oxygenates.

WO 03 020670 A1 provides a method for removing oxygenated componentssuch as acetaldehyde, CO2 and/or water from an olefin stream. Itexplains it is desirable to remove such oxygenated components, sincethey may poison catalysts that are used to further process olefincomposition. In addition, the presence of certain oxygenated compounds,such as acetaldehyde, can cause fouling in other olefin purificationunits, e.g., acid gas treating units. The method comprises providing anolefin stream containing ethylene, propylene, C4+ olefins andacetaldehyde. The olefin stream is separated into a first fraction and asecond fraction, wherein the first fraction comprises at least amajority of the ethylene and/or propylene present in the olefin stream,and the second fraction comprises at least a majority of the C4+ olefinsand acetaldehyde present in the olefin stream. The first fraction isthen acid gas treated by sodium hydroxide or potassium hydroxide. Theolefin stream is separated by distillation, preferably, the distillationis extractive distillation using an extractant. The preferred extractantis a polar composition having an average boiling point of at least 38°C. at 1 atm. Methanol is one type of preferred extractant.

WO 03 020672 A1 describes method of removing dimethyl ether from anethylene and/or propylene containing stream. The olefin stream is passedto a water absorption column, methanol is used as the water absorbent.Methanol and entrained water, as well as some oxygenated hydrocarbon, isrecovered as the bottoms stream of said water absorption column, anoverhead olefin is recovered and sent to a distillation column. Thedistillation column separates ethylene and propylene, as well as lighterboiling point components from the dimethyl ether and heavier boilingpoint components, including C4+ components and methanol remaining fromthe methanol wash. Additional methanol is added to the distillationcolumn to reduce clathrate and/or free water formation in thedistillation column. The ethylene and propylene containing stream exitsthe distillation column as overhead and the heavier boiling pointcomponents which include the dimethyl ether and C4+ components exit thedistillation column as the bottoms. Ethylene and propylene then flow toa caustic wash column.

WO 03 033438 A1 describes a method for processing an olefin streamcontaining oxygenates and water, comprising: providing an olefin streamcontaining oxygenates and water; dewatering the olefin stream;compressing the dewatered olefin stream; washing the olefin stream withmethanol to remove at least a portion of the oxygenate from the olefinstream; contacting the methanol washed olefin stream with water; andfractionating the water contacted olefin stream. The revovered olefinstream (washed with methanol and then with water) is further sent to analkali wash and a drying step. The olefin stream containing oxygenatesand water is the effluent of an MTO process.

U.S. Pat. No. 6,444,869 describes a process for the production ofethylene from an oxygenate conversion effluent stream. The oxygenateconversion effluent stream comprises hydrogen, methane, ethylene,ethane, propylene, propane and C4+ olefins. This effluent is compressed,treated to remove oxygenates, passed to a carbon dioxide removal zonewherein carbon dioxide is absorbed by contacting a caustic solution orby contacting an amine solution in combination with a caustic solutionin a conventional manner to remove the carbon dioxide, dried, thenfractionation is made through a deethanizer and a demethanizer.

US 2005-0283038 A1 described a process for producing an olefins streamfrom a first vapor effluent stream from an oxygenate to olefinconversion reaction, said first vapor effluent stream comprising C2 andC3 olefins, C4 hydrocarbons, and C2 to C6 carbonyl compounds. In theprocess, the temperature and pressure of the first vapor effluent streamare adjusted to produce a second vapor effluent stream having a pressureranging from about 100 psig to about 350 psig (790 to 2514 kPa) and atemperature ranging from about 70° F. to about 120° F. (21 to 49° C.),said second vapor effluent stream containing about 50 wt. % or more C4hydrocarbons based upon the total weight of C4 hydrocarbons in the firstvapor effluent stream. The second vapor effluent stream is then washedwith a liquid alcohol-containing stream to produce a third vaporeffluent stream, whereafter the third vapor effluent stream is washedwith liquid water to provide a fourth vapor effluent stream comprisingthe C2 and C3 olefins and about 1.0 wt. % or less C2 to C6 carbonylcompounds. In one embodiment of such a recovery process, at least partof the fourth vapor effluent stream is contacted with a basic component,such as caustic or an amine, to remove the bulk of the carbon dioxidetherefrom (thus removing “acid gas” from the fourth vapor effluentstream), whereafter the CO₂-depleted stream is dried.

The main drawback of the above prior arts is the fouling of the causticscrubber. The inlet gas to the caustic scrubber contains reactiveoxygenates like aldehydes and ketones. These aldehydes react in thealdol condensation reaction in the caustic tower environment to formsignificant red oil polymers. This causes significant fouling concernsin the caustic tower which impact the unit run length. The spent caustictreatment with significant red oil polymer content is also an importantconcern as well as the spent caustic treatment and disposal issues. Inaddition there are the handling and disposal issues of red oil polymers.

It has now been discovered a process for removing oxygenatedcontaminants from an ethylene stream wherein there is no caustic wash toremove the CO2 and no wash column to remove the oxygenates.

BRIEF SUMMARY OF THE INVENTION

The present invention is, in a first embodiment, a process for removingoxygenated contaminants from an ethylene stream comprising:

-   a) providing a dried ethylene stream (A) comprising essentially    ethylene, up to 1 w % oxygenates, ethane, CO, CO2, H2, CH4 and C3+    hydrocarbons,-   b) sending said stream (A) to a stripper (also referred to as a    demethanizer) to produce-   an overhead stream comprising essentially CO, H2 and CH4,-   a bottom stream comprising essentially ethylene, oxygenates, ethane,    CO2 and C3+ hydrocarbons, and-   (i)-   c) sending said bottom stream of step b) to a deethanizer to produce    a bottom stream comprising essentially ethane, oxygenates and C3+    hydrocarbons,-   an overhead stream consisting essentially of ethylene and CO2,-   d) sending said overhead of step c) to a fixed bed CO2 adsorption    zone to recover an ethylene stream essentially free of CO2,-   or (ii)-   c1) sending said bottom stream of step b) to a fixed bed CO2    adsorption zone to recover a stream essentially free of CO2, then    sending said stream to a deethanizer to produce-   a bottom stream comprising essentially ethane, oxygenates and C3+    hydrocarbons,-   an overhead stream consisting essentially of ethylene essentially    free of CO2.

The above process is referred to as embodiment 1.

In a second embodiment the deethanizer of embodiment 1 is replaced bytwo C2 splitters.

Said second embodiment is a process for removing oxygenated contaminantsfrom an ethylene stream comprising:

-   a) providing a dried ethylene stream (A) comprising essentially    ethylene, up to 1 w % oxygenates, ethane, CO, CO2, H2, CH4 and C3+    hydrocarbons,-   b) sending said stream (A) to a stripper (also referred to as a    demethanizer) to produce-   an overhead stream comprising essentially CO, H2 and CH4,-   a bottom stream comprising essentially ethylene, oxygenates, ethane,    CO2 and C3+ hydrocarbons, and-   (i)-   c) sending said bottom stream of step b) to a primary C2 splitter to    produce a bottom stream comprising essentially ethane, oxygenates,    C3+ hydrocarbons and a portion of ethylene,-   an overhead stream consisting essentially of ethylene and CO2,-   d) sending said overhead of step c) to a fixed bed CO2 adsorption    zone to recover an ethylene stream essentially free of CO2,-   e) sending the bottom stream of step c) to a secondary C2 splitter    to produce a bottom stream comprising essentially ethane, oxygenates    and C3+ hydrocarbons,-   an overhead stream consisting essentially of ethylene, optionally    recycled to the production zone of stream (A),-   Or (ii)-   c1) sending said bottom stream of step b) to a fixed bed CO2    adsorption zone to recover a stream essentially free of CO2, then    sending said stream to a primary C2 splitter to produce-   a bottom stream comprising essentially ethane, oxygenates, C3+    hydrocarbons and a portion of ethylene,-   an overhead stream consisting essentially of ethylene essentially    free of CO2,-   e1) sending the bottom stream of step c1) to a secondary C2 splitter    to produce-   a bottom stream comprising essentially ethane, oxygenates and C3+    hydrocarbons,-   an overhead stream consisting essentially of ethylene, optionally    recycled to the production zone of stream (A).

In a third embodiment the demethanizer (stripper) of embodiment 1 isreplaced by two demethanizers.

Said third embodiment is a process for removing oxygenated contaminantsfrom an ethylene stream comprising:

-   a) providing a dried ethylene stream (A) comprising essentially    ethylene, up to 1 w % oxygenates, ethane, CO, CO2, H2, CH4 and C3+    hydrocarbons,-   b) sending said stream (A) to a primary demethanizer to produce-   an overhead stream comprising essentially CO, H2, CH4 and a portion    of ethylene and ethane,-   a bottom stream comprising essentially ethylene, oxygenates, ethane,    CO2 and C3+ hydrocarbons,-   c) sending said overhead stream of step b), optionally through a    compressor, to a secondary demethanizer to produce-   an overhead stream comprising essentially CO, H2 and CH4,-   a bottom stream comprising essentially ethylene, oxygenates, ethane,    CO2 and C3+ hydrocarbons, and-   (i)-   d) sending said bottom stream of step b) and said bottom stream of    step c) to a C2 splitter to produce-   a bottom stream comprising essentially ethane, oxygenates and C3+    hydrocarbons,-   an overhead stream consisting essentially of ethylene and CO2,-   e) sending said overhead of step d) to a fixed bed CO2 adsorption    zone to recover an ethylene stream essentially free of CO2,-   or (ii)-   d1) sending said bottom stream of step b) and said bottom stream of    step c) to a fixed bed CO2 adsorption zone to recover a stream    essentially free of CO2, then sending said stream to a C2 splitter    to produce-   a bottom stream comprising essentially ethane, oxygenates and C3+    hydrocarbons,-   an overhead stream consisting essentially of ethylene essentially    free of CO2.

In an embodiment the weight ratio of ethane+CO+CO2+H2+CH4+C3+hydrocarbons to ethylene in (A) is less than 10/90.

In an embodiment the weight ratio of ethane+CO+CO2+H2+CH4+C3+hydrocarbons to ethylene in (A) is less than 10/90 and above 0.1/99.9.

In an embodiment the weight ratio of ethane+CO+CO2+H2+CH4+C3+hydrocarbons to ethylene in (A) is less than 5/95.

In an embodiment the proportion of oxygenates in (A) is from 50 wppm to7000 wppm.

In an embodiment the proportion of oxygenates in (A) is up to 3000 wppm.

In an embodiment the proportion of oxygenates in (A) is up to 2000 wppm.

In an embodiment the proportion of H2 in (A) is from 5 to 1000 wppm.

In an embodiment the proportion of H2 in (A) is up to 800 wppm.

In an embodiment the proportion of H2 in (A) is up to 500 wppm.

Advantageously “dried ethylene stream” at step a) means a water contentless than 5 wppm, advantageously less than 3 wppm and preferably lessthan 1 wppm.

In an embodiment when the dried ethylene stream (A) has been made byethanol dehydration said stream (A) contains substantially no acetylene.

Ethylene treated in accordance with this invention is particularlysuitable for use as feedstock for making alpha-olefins,ethylbenzene/styrene, ethyleneoxide/ethyleneglycol, ethylenedichlorideand corresponding polymers, like polyethylene homo or copolymer (PE,EPR, EPDM etc), polystyrene (PS), styrene copolymers with butadiene,isoprene, acrylonitrile or combinations (SBS, SIS, SBR, ABS, SAN),polyesters (PET) and polyvinylchlorides (PVC).

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 depicts a process according to the first embodiment with thestripper (demethanizer), the CO2 adsorbers, and the deethanizer.

FIG. 2 depicts a process according to the second embodiment with thedemethanizer, the CO2 adsorbers, the primary C2 splitter, and thesecondary C2 splitter.

FIG. 3 depicts a process according to the third embodiment with theprimary demethanizer, the CO2 adsorbers, the secondary demethanizer, theC2 splitter, and the compressor.

FIG. 4 depicts a process derived from the first embodiment shown in FIG.1, in which condensers and reboilers are inserted.

DETAILED DESCRIPTION OF THE INVENTION

As regards the oxygenated contaminants also referred to as oxygenates,one can cite ethanol, C3 alcohols; ethers such as diethylether andmethyl ethyl ether; carboxylic acids such as acetic acid; aldehydes suchas acetaldehyde; ketones such as acetone; and esters such as methylesters. Particularly problematic oxygenate contaminants in an alcoholdehydration are aldehydes.

As regards the ethylene stream (A) of step a), it can be originatingfrom the dehydration of ethanol. Said dehydration can be made in one ormore ethanol dehydration reactors. As regards alcohol dehydration, suchprocess is described in WO-2009-098262, WO-2009-098267, WO-2009-098268and WO-2009-098269 the content of which is incorporated in the presentapplication. The present invention is very efficient for thepurification of ethylene produced by dehydration of ethanol.

The outlet of said dehydration reactor comprises essentially ethyleneand steam as well as minor amounts of oxygenates, ethane, CO, CO2, H2,CH4 and C3+ hydrocarbons. “Minor amounts” means the weight ratio ofethane+CO+CO2+H2+CH4+C3+ hydrocarbons to ethylene is less than 20/80 andmost of time less than 10/90.

Said outlet of dehydration reactor is initially cooled, typically in aquench tower employing water as the quench medium. In the quench tower,most of the water contained in the outlet of dehydration reactor iscondensed and is removed from the bottom of the tower as a liquid waterbottom stream. A part of said water bottom stream is cooled in a heatexchanger and recycled as quenching medium to the top of the quenchcolumn. The part of the water bottom stream which is not recycled asquenching medium may contain a part of the oxygenates and mostlyunconverted ethanol if any. Said stream can be treated in a strippingcolumn to recover a pure water stream. Ethylene, oxygenates, ethane, CO,CO2, H2, CH4 and C3+ hydrocarbons are removed from the top of the quenchtower at a pressure typically such as 1 to 16 bars absolute and arereferred to as the contaminated ethylene stream. Advantageously saidcontaminated ethylene stream is successively compressed and cooled inone or more steps to remove the major part of water, further fed to afixed bed drying zone and finally to the process of the invention.

In the previous compression steps the recovered water contains a part ofthe oxygenated contaminants and hydrocarbons dissolved. The contaminatedhydrocarbon stream can also be cooled before the first compression stepand water recovered. In an embodiment the water recovered upon eachcooling further to a compression step and upon cooling, if any, beforethe first compression step is sent to a stripping column to produce anoverhead stream comprising essentially oxygenated contaminants andhydrocarbons and an essentially pure water bottoms stream. Optionallythe overhead stream is burned to destroy the oxygenated contaminants andrecover heat.

After the compression steps the contaminated ethylene stream is furtherfed to a fixed bed drying zone and finally to the process of the presentinvention. The fixed bed drying zone is known in itself.

As regards the fixed bed CO2 adsorption zone, it can be any componentcapable to selectively remove CO2. By way of example it is an availablecommercial fixed bed adsorption (PSA for pressure swing adsorption orTSA for temperature swing adsorption) using molecular sieves or basicoxides, supported basic oxides, high surface area carbons,organo-metallic framework components (MOF's) or mixture thereof. Themolecular sieves are preferably low silica zeolites, having 8 (amongwhich zeolite A) or 12 membered (among which zeolite X) rings andexchanged with alkali, alkaline earth or lanthanide cations. Othermolecular sieves are crystalline titanosilicates (ETS family materials).Supported basic oxides are preferably, alkali, alkaline earth orlanthanide oxides supported on high surface area carbons, alumina,silica, zirconia or titania. The removal of CO2 can be carried out witha liquid stream or with a gaseous ethylene stream depending on thepressure and temperature. A stream essentially free of CO2 is recovered.As only trace amounts of CO2 have to be removed from the ethylene, thepreferred process cycle is of the thermal swing adsorption (TSA) type.Said fixed bed adsorbent, once saturated with CO2, can be regenerated,during regeneration the desorption produces a stream which can betreated anywhere. In a TSA process cycle, the regeneration is done whilesweeping the saturated adsorbent with an inert gas by increasing thetemperature until desorption of the CO2 occurs. Eventually the saturatedadsorbent can be replaced by new adsorbent and the saturated adsorbenteither be disposed of or regenerated ex-situ for further use.“Essentially” has to be interpretated in the light of the further use ofethylene. Should ethylene is to be polymerized CO2 has to be 1 ppm volor less and preferably 0.5 ppm vol or less.

As regards the demethanizer, it is also referred to as a stripper infirst and second embodiments and as a primary and secondary demethanizerin the third embodiment. The purpose of said demethanizer is to recoveran overhead comprising essentially H2, CH4 and CO. It is advantageouslya distillation column.

As regards the operating conditions, the demethanizer has to be at apressure high enough to operate at temperatures which are not too low. Ademethanizer to recover an overhead comprising H2, CH4 and CO andessentially liquid ethylene at the bottoms operating at 40 barg has anoverhead temperature of around 0 to −10° C. and a bottom temperature ofaround 0° C. The same demethanizer operating at 21 barg has an overheadtemperature of −30° C. and a bottom temperature of around −24° C. Thesetemperatures and pressures are a function of the proportion of H2, CH4and CO in the ethylene stream (A) and mainly of the proportion of H2.

In an embodiment the pressure of the C2 splitter also referred to as adeethanizer is selected to have a temperature of the C2splitter/deethanizer bottoms such as there is no oligomerization orpolymerization of the oxygenates. By way of example said temperatureshould not exceed 150° C. and advantageously not exceed 100° C. Thistemperature is function of the pressure and of the proportion ofoxygenates in the mixture of oxygenates+ethane+C3+ hydrocarbons. Thehigher the proportion of oxygenates the higher the temperature. Thehigher the pressure the higher the temperature. The C2splitter/deethanizer is advantageously a distillation column.

As regards the first embodiment and the stripper, it is advantageously adistillation column. The overhead is a mixture of essentially CO, H2 andCH4. The deethanizer is advantageously a distillation column. The fixedbed CO2 adsorption zone can be an available commercial fixed bedadsorption (TSA or PSA) as described above. A stream essentially free ofCO2 is recovered.

In an embodiment the stripper (demethanizer) and the C2splitter/deethanizer are operating at the same pressure except thepressure drop between the demethanizer and the C2 splitter/deethanizerfor transfer of fluids. Advantageously the pressure is ranging from 15to 45 barg.

A process according to the first embodiment is described on FIG. 1wherein 1 is the stripper (demethanizer), 2 and 3 the CO2 adsorbers and4 the deethanizer. On top of the stripper there are a condenser, adecanter producing a liquid phase sent as a reflux to said stripper anda gaseous phase which is the overhead, they are not shown on the FIG. 1.On the bottom of the stripper there is a reboiler not shown on FIG. 1.The deethanizer has a similar equipment not shown on FIG. 1. Thecontaminated ethylene stream (A) comprising essentially ethylene, up to1 w % oxygenates, ethane, CO, CO2, H2, CH4 and C3+ hydrocarbons has beendried and sent to the stripper 1 (also referred to as a demethanizer) toproduce

-   an overhead stream comprising essentially CO, H2 and CH4,-   a bottom stream comprising essentially ethylene, oxygenates, ethane,    CO2 and C3+ hydrocarbons,-   said bottom stream of the stripper 1 is sent to the deethanizer 4 to    produce-   a bottom stream comprising essentially ethane, oxygenates and C3+    hydrocarbons,-   an overhead stream consisting essentially of ethylene and CO2,-   said overhead of deethanizer 4 is sent to a fixed bed CO2 adsorption    zone 2 and 3 to recover an ethylene stream essentially free of CO2.

In a specific example the pressure of the stripper ranges from 15 to 30barg and the pressure of the deethanizer and the CO2 adsorbers is about1 or 2 barg less corresponding to the pressure drop due to pipes andequipment. In this range of pressure the temperature on top of stripperand after the condenser ranges from −20 to −30° C., the temperature onbottom of stripper ranges from −15 to −25° C., the temperature on top ofdeethanizer and after the condenser ranges from −30 to −20° C. and thetemperature on bottom of deethanizer ranges from 75 to 85° C.

Preferably the pressure of the stripper ranges from 20 to 25 barg andthe pressure of the deethanizer and the CO2 adsorbers is about 1 or 2barg less corresponding to the pressure drop due to pipes and equipment.In this range of pressure the temperature on top of stripper and afterthe condenser ranges from −22 to −26° C., the temperature on bottom ofstripper ranges from −20 to −24° C., the temperature on top ofdeethanizer and after the condenser ranges from −27 to −22° C. and thetemperature on bottom of deethanizer ranges from 78 to 82° C.

In another specific example the pressure of the stripper ranges from 35to 45 barg and the pressure of the deethanizer and the CO2 adsorbers isabout 15 to 25 barg less. Advantageously the pressure of the deethanizerranges from 15 to 25 barg. In this range of pressure the top of stripperis at a temperature in the range −10 to 0° C. and condensed at atemperature ranging from −35 to −45° C., the temperature on bottom ofstripper ranges from −5 to 5° C., the temperature on top of deethanizerranges from −25 to −35° C., is condensed at a temperature in the range−25 to −35° C. and the temperature on bottom of deethanizer ranges from75 to 85° C.

Preferably the pressure of the stripper ranges from 38 to 42 barg andthe pressure of the deethanizer and the CO2 adsorbers ranges from 17 to22 barg. In this range of pressure the top of stripper is at atemperature in the range −8 to −2° C. and condensed at a temperatureranging from −38 to −42° C., the temperature on bottom of stripperranges from 0 to 5° C., the temperature on top of deethanizer rangesfrom −28 to −32° C., is condensed at a temperature in the range −28 to−32° C. and the temperature on bottom of deethanizer ranges from 78 to82° C.

As regards the second embodiment and the demethanizer, it isadvantageously a distillation column. The primary and secondarysplitters are each advantageously a distillation column. The fixed bedCO2 adsorption zone has already been described above. A streamessentially free of CO2 is recovered.

In an embodiment the demethanizer and the primary and secondary C2splitter/deethanizer are operating at the same pressure except thepressure drop for transfer of fluids. Advantageously the pressure isranging from 15 to 45 barg.

A process according to the second embodiment is described on FIG. 2wherein 1 is the demethanizer, 2 and 3 the CO2 adsorbers, 4 the primaryC2 splitter and 5 the secondary C2 splitter. On top of the demethanizerthere are a condenser, a decanter producing a liquid phase sent as areflux to said demethanizer and a gaseous phase which is the overhead,they are not shown on the FIG. 2. On the bottom of the demethanizerthere is a reboiler not shown on FIG. 2. The primary C2 splitter and thesecondary C2 splitter have each a similar equipment not shown on FIG. 2.

The contaminated ethylene stream (A) comprising essentially ethylene, upto 1 w % oxygenates, ethane, CO, CO2, H2, CH4 and C3+ hydrocarbons hasbeen dried and sent to the demethanizer 1

-   to produce-   an overhead stream comprising essentially CO, H2 and CH4,-   a bottom stream comprising essentially ethylene, oxygenates, ethane,    CO2 and C3+ hydrocarbons,-   said bottom stream of demethanizer 1 are sent to the primary C2    splitter 4 to produce-   a bottom stream comprising essentially ethane, oxygenates, C3+    hydrocarbons and a portion of ethylene,-   an overhead stream consisting essentially of ethylene and CO2,-   said overhead of the primary C2 splitter 4 is sent to a fixed bed    CO2 adsorption zone 2 and 3 to recover an ethylene stream    essentially free of CO2,-   the bottom stream of the primary C2 splitter 4 is sent to a    secondary C2 splitter 5 to produce-   a bottom stream comprising essentially ethane, oxygenates and C3+    hydrocarbons,-   an overhead stream consisting essentially of ethylene, optionally    recycled to the production zone of stream (A).

In a specific example the pressure of the demethanizer ranges from 35 to45 barg and the pressure of the primary C2 splitter and the CO2adsorbers is about 1 or 2 barg less corresponding to the pressure dropdue to pipes and equipment. The pressure of the secondary C2 splitterranges from to 15 to 25 barg. In these ranges of pressure the top ofdemethanizer is at a temperature in the range −10 to 0° C., is condensedat a temperature ranging from −35 to −45° C., the temperature on bottomof demethanizer ranges from −5 to 5° C., the top of the primary C2splitter is in a temperature range from −5 to 5° C., is condensed in atemperature range from −5 to 5° C., the temperature on bottom of primaryC2 splitter ranges from 75 to 85° C., the top of the secondary C2splitter is in a temperature range from −25 to −35° C., is condensed ina temperature range from −25 to −35° C. and the temperature on bottom ofsecondary C2 splitter ranges from 75 to 85° C.

Preferably the pressure of the demethanizer ranges from 38 to 42 bargand the pressure of the primary C2 splitter and the CO2 adsorbers isabout 1 or 2 barg less corresponding to the pressure drop due to pipesand equipment. The pressure of the secondary C2 splitter ranges from to18 to 22 barg. In these ranges of pressure the top of demethanizer is ina temperature range of −8° C. to −2° C., is condensed at a temperatureranging from −38 to −42° C., the temperature on bottom of demethanizerranges from 0 to 4° C., the top of primary C2 splitter is in atemperature range from −4 to 0° C., is condensed in a temperature rangefrom −4 to 0° C., the temperature on bottom of primary C2 splitterranges from 78 to 82° C., the top of the secondary C2 splitter is in atemperature range from −28 to −32° C., is condensed in a temperaturerange from −28 to −32° C., and the temperature on bottom of secondary C2splitter ranges from 78 to 82° C.

As regards the third embodiment and the primary and secondarydemethanizer, they are each advantageously a distillation column. The C2splitter is advantageously a distillation column. The fixed bed CO2adsorption zone has already been described above. A stream essentiallyfree of CO2 is recovered.

In an embodiment the primary, the secondary demethanizers and the C2splitter/deethanizer are operating at the same pressure except thepressure drop for transfer of fluids. Advantageously the pressure isranging from 15 to 45 barg.

A process according to the third embodiment is described on FIG. 3wherein 1 is the primary demethanizer, 2 and 3 the CO2 adsorbers, 4 thesecondary demethanizer, 5 the C2 splitter and 6 the compressor. On topof the primary demethanizer there are a condenser, a decanter producinga liquid phase sent as a reflux to said primary demethanizer and agaseous phase which is the overhead, they are not shown on the FIG. 3.The overhead of the primary demethanizer is sent to the compressor. Onthe bottom of the primary demethanizer there is a reboiler not shown onFIG. 3. The secondary demethanizer and the C2 splitter have each asimilar equipment not shown on FIG. 3.

The contaminated ethylene stream (A) comprising essentially ethylene, upto 1 w % oxygenates, ethane, CO, CO2, H2, CH4 and C3+ hydrocarbons hasbeen dried is sent to a primary demethanizer 1 to produce

-   an overhead stream comprising essentially CO, H2, CH4 and a portion    of ethylene and ethane,-   a bottom stream comprising essentially ethylene, oxygenates, ethane,    CO2 and C3+ hydrocarbons,-   the overhead stream of demethanizer 1 is sent through a compressor 6    to a secondary demethanizer 4 to produce-   an overhead stream comprising essentially CO, H2 and CH4,-   a bottom stream comprising essentially ethylene, oxygenates, ethane,    CO2 and C3+ hydrocarbons,-   said bottom stream of secondary demethanizer 4 and said bottom    stream of primary demethanizer 1 are sent to a C2 splitter 5 to    produce-   a bottom stream comprising essentially ethane, oxygenates and C3+    hydrocarbons,-   an overhead stream consisting essentially of ethylene and CO2,-   said overhead of the C2 splitter 5 is sent to a fixed bed CO2    adsorption zone 2-3 to recover an ethylene stream essentially free    of CO2.

In a specific example the pressure of the primary demethanizer rangesfrom 15 to 25 barg, the pressure of the secondary demethanizer rangesfrom 40 to 50 barg, the pressure of the C2 splitter is essentially atthe same pressure as the primary demethanizer except the pressure dropfor transfer of fluids and ranges from 15 to 25 barg and the pressure ofthe CO2 adsorbers is about 1 or 2 barg less corresponding to thepressure drop due to pipes and equipment. In these ranges of pressurethe top of the primary demethanizer is in a temperature range of −25 to−35° C., condensed at a temperature ranging from −25 to −35° C., thetemperature in the bottom of the primary demethanizer ranges from −30 to−20° C., the top of the secondary demethanizer is in a temperature rangeof −10 to 0° C., is condensed at a temperature ranging from −30 to −40°C., the temperature in the bottom of the secondary demethanizer rangesfrom 0 to 10° C., the top of the C2 splitter is in a temperature rangefrom −25 to −35° C., is condensed in a temperature range from −25 to−35° C., and the temperature in the bottom of the C2 splitter rangesfrom 75 to 85° C.

Preferably the pressure of the primary demethanizer ranges from 18 to 22barg, the pressure of the secondary demethanizer ranges from 43 to 47barg, the pressure of the C2 splitter is essentially at the samepressure as the primary demethanizer except the pressure drop fortransfer of fluids and ranges from 18 to 22 barg and the pressure of theCO2 adsorbers is about 1 or 2 barg less corresponding to the pressuredrop due to pipes and equipment. In these ranges of pressure the top ofthe primary demethanizer is in a temperature range of −25 to −31° C.,condensed at a temperature ranging from −27 to −32° C., the temperaturein the bottom of the primary demethanizer ranges from −28 to −22° C.,the top of the secondary demethanizer is in a temperature range of −6 to−2° C., condensed at a temperature ranging from −30 to −35° C., thetemperature in the bottom of the secondary demethanizer ranges from 3 to8° C., the top of the C2 splitter is in a temperature range from −28 to−32° C., is condensed in a temperature range from −28 to −32° C., andthe temperature in the bottom of the C2 splitter ranges from 78 to 82°C.

EXAMPLES

The process according to FIG. 4 is operated. FIG. 4 is derived from FIG.1 by insertion of condensers and reboilers. The results are on thefollowing table.

stream No on FIG. 4 1 2 3 Stripper Stripper Stripper feed bottoms purgeTemperature ° C. 15 −20 −24 Pressure bar g 22 22 22 H2 kg/h 0.1 0.1 COkg/h 1 1 CO2 kg/h 1 1 ethane kg/h 5 5 ethylene kg/h 25091 25013 78acetaldehydes kg/h 18 18 C3+ kg/h 325 325 Total kg/h 25441.1 25362 79.1stream No on FIG. 4 5 6 4 Deethanizer Ethylene Deethanizer vapor productbottoms distillate Temperature ° C. 80 −24 20 Pressure bar g 21 21 20 H2kg/h CO kg/h CO2 kg/h 1 ethane kg/h 5 5 ethylene kg/h 18 24995 24995acetaldehydes kg/h 18 C3+ kg/h 325 Total kg/h 361 25001 25000

The invention claimed is:
 1. A process for removing oxygenated contaminants from an ethylene stream comprising: a) providing a dried ethylene stream (A) comprising essentially ethylene, up to 1 w % oxygenates, ethane, CO, CO₂, H₂, CH₄ and C₃₊ hydrocarbons; b) sending the dried ethylene stream stream (A) to a stripper to produce an overhead stream comprising essentially CO, H₂ and CH₄; and a bottom stream comprising essentially ethylene, oxygenates, ethane, CO₂ and C₃₊ hydrocarbons; and performing step (i) or step (ii); wherein step (i) comprises: c) sending the bottom stream of step b) to a primary C₂ splitter to produce a bottom stream comprising essentially ethane, oxygenates, C₃₊ hydrocarbons and a portion of ethylene; and an overhead stream consisting essentially of ethylene and CO₂; d) sending the overhead of step c) to a fixed bed CO₂ adsorption zone to recover an ethylene stream essentially free of CO₂; e) sending the bottom stream of step c) to a secondary CO₂ splitter to produce a bottom stream comprising essentially ethane, oxygenates and C₃₊ hydrocarbons; and an overhead stream consisting essentially of ethylene, optionally recycled to a production zone of the dried ethylene stream (A); wherein step (ii) comprises: c1) sending the bottom stream of step b) to a fixed bed CO₂ adsorption zone to recover a stream essentially free of CO₂, then sending the stream essentially free of CO₂ to a primary CO₂ splitter to produce a bottom stream comprising essentially ethane, oxygenates, C₃₊ hydrocarbons and a portion of ethylene; and an overhead stream consisting essentially of ethylene essentially free of CO₂; e1) sending the bottom stream of step c1) to a secondary CO₂ splitter to produce a bottom stream comprising essentially ethane, oxygenates and C₃₊ hydrocarbons; and an overhead stream consisting essentially of ethylene, optionally recycled to the production zone of the dried ethylene stream (A).
 2. The process of claim 1, wherein the fixed bed CO₂ adsorption zone is located at an inlet of the primary C₂ splitter.
 3. The process of claim 1, wherein a weight ratio of ethane+CO+CO₂+H₂+CH₄+C₃+hydrocarbons to ethylene in the dried ethylene stream (A) is less than 10/90.
 4. The process of claim 3, wherein the weight ratio of ethane+CO+CO₂+H₂+CH₄+C₃+hydrocarbons to ethylene in the dried ethylene stream (A) is above 0.1/99.9.
 5. The process of claim 4, wherein the weight ratio of ethane+CO+CO₂+H₂+CH₄+C₃+hydrocarbons to ethylene in the dried ethylene stream (A) is less than 5/95.
 6. The process of claim 1, wherein a proportion of oxygenates in the dried ethylene stream (A) is from 50 wppm to 7000 wppm.
 7. The process of claim 1, wherein a proportion of oxygenates in the dried ethylene stream (A) is up to 3000 wppm.
 8. The process of claim 1, wherein the proportion of oxygenates in the dried ethylene stream (A) is up to 2000 wppm.
 9. The process of claim 1, wherein a proportion of H₂ in the dried ethylene stream (A) is from 5 to 1000 wppm.
 10. The process of claim 1, wherein a proportion of H₂ in the dried ethylene stream (A) is up to 800 wppm.
 11. The process of claim 1, wherein a proportion of H₂ in the dried ethylene stream (A) is up to 500 wppm.
 12. The process of claim 1, wherein the dried ethylene stream (A) is originated from the dehydration of ethanol. 